Obviously, my experience is very limited along these lines.
It seems like the Arriflex bayonet mount and the Eclair Cameflex mount have very little available in terms of lenses that can be directly mounted (correct me if I'm wrong). Since that seems to be the case, what should I be looking for in terms of adapters that would give me the most flexibility both in terms of lens choice and lens price? PL adapater, NikonF, Canon FD? Me confused...

A PL mount adapter would give you access to the best cine lenses in the world, both 16 and 35 mm's. It won't be cheap, though, neither the mount nor the lenses. Even renting PL mount lenses isn't cheap, unless you have a working budget. If you can find one cheap PL adapter, they are nice to have just in case.

Having a 35mm lens mount adapter is nice but has its caveats. The 16mm FOV will be dramatically reduced from what the lens would look like on a 35mm camera. So a 50mm 35mm lens will give you the FOV of a 100mm lens (more or less) when used on a S16 or 16 mm camera. One can argue that the image will be as good as it can, being that only the center (and sharpest) portion of the optics would be used, but it does have limitations.

Yes, you can use nice lenses on it, if you don't mind the FOV change. I have a c-mount to Nikon mount adapter I bought on eBay for $30, it works great. As an idea you can buy lenses that have been designed for APS-C chips and try those. Just make sure they have manual aperture settings!!!

Adapters are generally a great buy, just make sure they are one piece or as close as possible, I have seen some that are poorly designed and with a lot of screws. Eventually they just start loosening up and keeping them tight (and the picture in focus can be a drag.

As far as FFD, most work OK if the camera is to spec and the adapter builders know what they are doing. I have bought 2 PL mount to ACL adapters and they have worked great. Les Bosher or Visual Products carry them, I believe. You can check with them as to their FFD status when you order of course.

There are in fact a lot of lenses available in CA/Eclair and Arri Bayonet (or Arri Standard) lens mounts. Look for them on eBay, they're all over, in varying conditions, but some of them are real gems for the price. One of the great adavantage of the ACL is its lens mount system, and the flexibility it gives you.
Readily available are the ACL mounts Eclair made : the CA, of course, the Arri Bayo, the Arri Standard. They also made a Nikon mount for the ACL that is quite rare (but far more solid and precise than a Nikon-to-C would be). Custom-made ACL mounts have also been made by different shops : PL, Aaton,... also quite rare and expensive.
Photography lens are fine for filming, but the ergonomics might not be the best, nor their construction (unless you go for high-price lenses).
Look for traditional cine lenses of good quality and you may find them surprisingly affordable as more and more people rush for the PL mounts. Since you shoot Super-16, you may have trouble finding an affordable zoom lens (besides the Angénieux 15-150, which is sometimes -- but not always -- poor), but the Cooke Kinetal series of fixed focal lenses can give you very good picture quality at a cheap price in Arri St mount. Kinoptiks are very good too, but a bit cultish and quite expensive. Zeiss tend to be more expensive because of their reputation as the sharpest.
My advice with an ACL is : find the good and cheap lens that you want, than locate the adapter, if you don't already have it.
Best, B.

I've borrowed the lenses for my new C mount to Nikon. I had to go with what I could afford. One limitation is that in 35mm there doesn't seem to be many lenses under 28mm, or very few.

Boris, thanks as well.
I do have to say that I find very little to none in the way of lenses for CA (Cameflex) mounts. Perhaps I'm searching on Ebay with the wrong words, but I've tried, under cameras and photo, and find nothing but a manual.

Could you also confirm if you know: is an Arri B mount the same thing as an Arri bayonet mount?
I also have searched Ebay with those terms with very little returns. None with Arri Bayonet and only a few for Arri B

Thanks as always. Have a warm day. It's -25 here. But then again that's with the wind chill

Yes, the big limiting fqctor with photo lenses is tha they are meant to cover a 24x36mm frame and will thus appear to have twice their focal lengths when used to shoot 16mm. Combined with the fact that it's difficult to build a wide angle for a wide format like 35mm photo, this leaves you with hardly any affordable choice for wide angles, or even standard lenses.Help could come from the lenses designed for the smaller sensors of digital SLRs, but a lot of them don't have an aperture ring and the cheap ones are... cheaply made to say the least.

As for searching eBay for cine lenses, don't do your search by the mount, but by the brand name (or series name, like Kinetal instead of Cooke, since you probably wouldn't want to pay the price for their 35mm format Speed Panchros anyways). Make the search as broad as possible so you also get the results from those seller who don't know the technical details of what they sell (quite common in the 16mm format, and not necessarily a bad sign for the shape of the lens). Also, since you have an ACL, don't overlook the C-mount lenses - some of them are quite good, and you won't compete with the owners of Arris, Aaton, CPs, etc. for those. Most Angénieux C-mounts are so-so to ok as they can be quite old (50's even), but brands like Cooke and Kinoptik offered their excellent lenses in C-mount too. And Kern also made excellent lenses in their Switar range, including a good 10mm that covers S-16, but you have to make sure you get the Kerns that do not bear the inscription H16RX or RX on them, since those are specified to correct for the Bolex H16 RefleX's fixed prism (non-RX Kerns should be engraved with AR).As a rough rule of thumb, you can expect most fixed focal 16mm lenses of 15mm focal length and more to cover the S-16 frame. Some 12mm do, a few 10mm too, and below that is very rare (the Kinoptik 9 and even 5,7mm do, and both were made in C-mount).

I've borrowed the lenses for my new C mount to Nikon. I had to go with what I could afford. One limitation is that in 35mm there doesn't seem to be many lenses under 28mm, or very few.

Boris, thanks as well.I do have to say that I find very little to none in the way of lenses for CA (Cameflex) mounts. Perhaps I'm searching on Ebay with the wrong words, but I've tried, under cameras and photo, and find nothing but a manual.

Could you also confirm if you know: is an Arri B mount the same thing as an Arri bayonet mount?I also have searched Ebay with those terms with very little returns. None with Arri Bayonet and only a few for Arri B

Thanks as always. Have a warm day. It's -25 here. But then again that's with the wind chill

I am using Nikon lenses with my cameras (K-3 and Milliken with c-f adapter) The glass is good, but the problem is as you say wide angle - but also aperture. I have a 20mm and a Zenitar 16mm which are both good that I also use with my d700 for stills. They are both 2.8 :-( great wide angles for full frame, but of course not so wide for s16. 28mm would be even worse.

Hey Tom, I'm shooting on an ACL here in Chicago too - we should get together for a drink and talk shop one day..?

I feel like after a year I've stumbled onto the most economical way to get a nice variety of primes. I have one of Les's Nikon mounts that I use with a variety 24mm up to 105mm Nikons. Due to crop factor they give me the equivalent of 50mm to 200mm range on the ACL. The problems is that to get wider using Nikons, you have to get fish-eye lenses which are expensive and heavy. Instead you can get wide c-mount switar, angie, etc. lenses on ebay to use as your wide primes. There's always a few switar 10mm lenses for sale. You just have to be careful on those you don't get the bolex "RX" reflex versions because the focal length is wrong for the ACL. Basically not being stuck on using only one type of lens mount will allow you to get the greatest variety for your money.

I'm planning to eventually pick up a PL mount and rent some nice lenses, but I have to give the bank account a rest for a while first!

If you can post a picture of the Arri Bayonet mount you have, I might be able to tell you if ARRI standard mount lenses will work with it. Most should. If it is of a particular design, you can use the whole line of Cooke Kinetal or Cooke Speed Panchro lenses as well.

The Kinetals are beautiful, not too expensive, and were designed for 16mm. Not sure if your camera is regular 16 or Super 16, but the Kinetal lenses all cover both (R16 & S16) except the 9mm, which only covers regular 16. You can see images from them on my web site.

The Speed Panchros were originally 35mm lenses, but work with 16mm too.

There is a bit of confusion in the above posts. A 50mm lens is a 50mm lens, no matter if it is a Kinetal, Speed Panchro, Zeiss, Nikon, Whatever. It doesn't matter whether it is on a 16mm or 35mm camera, it is still a 50mm lens. Now, because the image area in 16mm is smaller than 35mm, you will be recording only the center image area coming in from the lens. But a 50mm Nikon lens which was designed for a Nikon still camera will give you the same image area on a 16mm camera as a Cooke Kinetal 50mm lens which was designed for a 16mm camera. It's just with the 16mm camera, the "normal range" of prime lenses goes from 9mm up to 50mm and the equivalent 35mm camera would have a "normal" prime lens range from 18mm up to 100mm. But a Cooke Kinetal 25mm lens(designed for a 16mm camera) will give the same image on a 16mm camera as a Cooke Speed Panchro 25mm lens(designed for a 35mm camera).

Also, if your mount can take the ARRI standard mount lenses, that opens you up to use Schneider lenses(usually a little soft), Angenieux lenses, the older Zeiss lenses, and even Rodenstock lenses if you come across any.

"A 50mm lens is a 50mm lens, no matter if it is a Kinetal, Speed Panchro, Zeiss, Nikon, Whatever. It doesn't matter whether it is on a 16mm or 35mm camera, it is still a 50mm lens."

Right, but the Field Of View (FOV) will change depending on the size of the aperture or sensor. So the 50mm lens will give you different angles of view if used on 16mm, 3-perf 35mm or 6 perf 35mm. Same lens - different FOV.